This present invention is related to an extendable antenna for a radio transceiver and more particularly to an antenna for a portable radio transceiver.
Extendable antennas have been developed to reduce the size of the portable radio tranceiver. A conventional antenna is shown in FIGS. 8, 9 and 10. In FIG. 10, a dash line shows the state of the antenna retracted into a housing 1 of a radio transceiver 2. This state is defined as a retracted mode in the description below. A two-dot chain line shows the state of the antenna extended. This state is defined as an extended mode. The extended mode is shown in FIG. 8. A printed circuit board 5 (a PC board 5) is disposed in the housing 1, and high frequency components are mounted on the PC board 5. A coupling member 7 is mounted on the PC board 5 and connected with a duplexer (not shown). The duplexer is connected with a transmitter and a receiver (not shown), also on the PC board 5. The duplexer, the transmitter and the receiver act as the circuitry of the transceiver 2.
A metal ring 9 has a female-screw portion and is inserted into the housing 1 and fitted. The coupling member 7 is connected with the metal ring 9. A holding member 11 has a male-screw portion, and the male-screw portion is screwed into the metal ring 9. The holding member 11 has some elastic tongues 11a for holding an antenna 3. Since the holding member 11 is metal, the coupling member 7 is electrically connected with the holding member 11.
The antenna 3 has a stopper portion 3a at a bottom portion, a top end cap 3b at a top portion, and a core portion 3c coupled to the stopper portion 3a and the top end cap 3b.
As shown in FIG. 8, when the antenna 3 is extended from the housing 1, the stopper portion 3a is engaged with a top of the tongues 11a and the stopper portion 3a is held by the tongues 11a. Since the stopper portion 3a and the core portion 3c are conductive material, the core portion 3c is electrically connected with the circuitry of the transceiver 2.
On the other hand, as shown in FIG. 9, when the antenna 3 is pushed down toward the housing 1, the top end cap 3b is held in the tongues 11a. In this state, the top end cap 3b is held by the toungues 11a. However, the top end cap 3b is plastic, therefore the antenna 3 is not electrically connected with the circuitry. Accordingly, the antenna 3 does not detect a radio frequency signal (RF signal) in the retracted mode.
When an operator does not wish to operate the transceiver, he often retracts the extendable antenna and thus reduces the antenna's projection to make the transceiver a suitable size for carrying. When the RF signal comes to the transceiver 2 in the retracted mode, the antenna 3 does not detect the RF signal. Therefore, to detect the RF signal, the operator must extend in advance the antenna 3 out of the housing.
To solve this deficiency, it is considered that a top end cap is conductive material and that the circuitry is electrically connected with the top end cap and an antenna core portion in the retracted mode. However, the electrical length of the top end cap is much less than the well known length of whip antennas having large gain (for example, a quarter wavelength). Accordingly the top end cap does not detect the RF signal. Furthermore in the retracted mode, almost all of the antenna core portion is located into the housing. However, there are shielding cases provided on the PC board to shield components (on the PC board) against interfering electric waves. These cases and the operator's hand interupt the RF signal which comes to the antenna core and therefore result in much reduction in a radiation efficiency. Accordingly the antenna core does not detect the RF signal.
To solve deficiency above, it is considered that the transceiver has an inner antenna and a rod antenna. The inner antenna way detect the RF signal when the rod antenna is retracted into the housing 10. However, the transceiver must detect the state in which the rod antenna is retracted and needs to have switching means for switching from the rod antenna to the inner antenna. Furthermore, the transceiver needs to have a conductive partition wall between the components and the inner antenna so that the components are not radiated by the inner antenna. Thus the transceiver needs to contain the inner antenna, the switching means and the conductive patition wall, therefore the size of the housing is large. Furthermore, the inner antenna is obliged to be disposed at an upper portion of the housing so that the inner antenna is not interrupted by the operator's hand when the RF signal comes to the transceiver. Therefore, other components may not disposed at the upper portion of the housing, as a result the inner antenna limits the area of possible location of the components.